China has not yet sent a spy ship to monitor the Rim of the Pacific exercise as it did in 2012 and 2014 -- but Russia has, U.S. Pacific Fleet confirmed.

The Balzam-class auxiliary general intelligence ship "recently" arrived in international waters off Hawaii, said Pacific Fleet spokesman Lt. Clint Ramsden.

"Obviously, we are aware that it is there, and we've taken all precautions necessary to protect our critical information," Ramsden said. "Its presence has not affected the conduct of the exercise."

Russia last participated in RIMPAC in 2012, Ramsden said. The country was invited in 2014, but declined, he said. Russia, at odds with the West over its annexation of Ukraine's Crimea peninsula, wasn't invited this year.

The last time a Russian spy ship stopped by Hawaii was in 2004, also coincident with RIMPAC, Pacific Fleet said.

Russia's AGI ship is outside of the U.S. 12-nautical-mile territorial waters, but within the U.S. 200-nautical-mile Exclusive Economic Zone. Pacific Fleet declined to say where the ship is operating in that zone, as well as which island it is near.

Pacific Fleet has "that information from an (intelligence) standpoint, but it's not something that we're disclosing at this time," Ramsden said.

U.S. Naval Institute News first reported the presence of the Russian spy ship.

In mid-January, amid a North Korean nuclear test, Russian bombers flying near Guam, and China's claims in the South China Sea, the Air Force said it was dispatching 12 F-16 Fighting Falcons to Guam's Andersen Air Force Base.

The temporary deployment followed the flight of two Russian strategic bombers in the vicinity of Guam on Nov. 25, and increasing probes -- usually with Cold War-era turboprop-powered Tu-95 "Bear" bombers -- off Guam, California and Alaska.

The fighter deployment to Guam was part of what's known as a "theater security package," scheduled months in advance, and was not related to any specific situation in the region, Hawaii-based Pacific Air Forces said at the time.

Russia has sought to reassert its military presence on the world stage with involvement in Syria and Cold War-style bomber flights near U.S. territory. Pacific Air Forces said at the time that no Russian bombers had flown near Hawaii in the past year.

At the same time China was invited into Pearl Harbor in 2014 to participate in Rim of the Pacific exercises for the first time (the exercise is held every two years), it also had a spy ship parked off Hawaii, Pacific Fleet reported two years ago.

The People's Liberation Army Navy auxiliary general intelligence ship also operated within the U.S. exclusive economic zone around Hawaii, but not within the territorial seas.

The Navy previously confirmed that China sent an AGI spy ship near Hawaii in 2012 during that year's RIMPAC exercise.

Then, as now, Pacific Fleet has had little heartburn with the presence of the foreign surveillance ships in international waters off Hawaii. The United States similarly operates off foreign shores.

"We continue to uphold the principle of freedom of navigation and overflight in accordance with international law," Ramsden said.

The United States and China continue to disagree over China's claim to much of the South China Sea, with the United States angering the rising Asian power with periodic "freedom of navigation" demonstrations in international waters in the region.

Twenty-six nations, 45 ships, five submarines, more than 200 aircraft and 25,000 personnel are participating in the biennial RIMPAC exercise running to Aug. 4, mostly in and around the Hawaiian Islands but also off Southern California.

The in-harbor planning phase continues this week with ships getting under way on Monday and in succeeding days for at-sea exercises.